1. Field of the Invention
This invention relates to carburetor mechanisms and more particularly to a fail-safe mixture control device for an updraft carburetor used on a normally aspirated aircraft engine.
2. Background of the Invention
Small aircraft which have normally aspirated engines are usually equipped with an updraft carburetor which, among other things, is provided with a mixture control valve. The mixture control valve is in the form of a rotary gate valve located within the fuel reservoir bowl of the carburetor and has a shaft extending externally of the carburetor body. A lever is attached to the extending end of the valve shaft and is movable through an arc of somewhat less than 90.degree. from the full lean to full rich positions. One end of a control cable is attached to the valve lever with the opposite end having a suitable knob thereon, with the knob being suitably mounted in the cockpit area of the aircraft.
The valve shaft and attached lever are oriented on the carburetor body in a way which would cause the gate valve to rotate to a full lean mixture setting, due to gravitational forces and engine vibrations, were it not for the control cable. Thus, in the event of control cable failure, the carburetor will automatically and ultimately move to a full lean fuel-air mixture setting.
As is well known, flying, landing and general aircraft operation at low density altitudes requires a relatively lean fuel-air mixture ratio. Low density altitudes, which are determined by altitude, temperature and barometric pressure, normally occur at altitudes of approximately 5,000 ft., or more, indicated mean sea level. Even so, control cable failure, as described above, will present a safety hazard in low density altitude flying as well as in high density altitude flying (usually below 5,000 ft. M.S.L.) in that when the mixture control valve is in the full lean mixture setting, the aircraft engine will be starved for fuel and engine failure will result.
It will now be seen that the above described prior art mixture control system presents a safety hazard in all flying situations.
If the prior art mixture control mechanism were configured in a way so that cable failure caused the gate valve to move to a full rich fuel-air mixture ratio setting, the problem would not be as critical in that some loss in power and performance would be experienced at high altitudes but a high altitude landing could be made, and no power and performance loss would be experienced in low altitude flying.
To the best of my knowledge, no method or device has been devised or suggested which would cause the mixture control valve of an updraft carburetor on a normally aspirated aircraft engine to move toward the full rich fuel-air mixture position in the event of control cable failure.
Therefore, a need exists for a fail-safe carburetor mixture control mechanism which eliminates, or at least substantially reduces, the safety hazard of the prior art.